Transcript for FBI Launches Investigation in to Death of Michael Brown

We begin with that FBI investigation now being launched after an unarmed teenager was shot in a St. Louis street. So many questions about how it happened and what led up to that moment. Overnight we saw the images, anger spiraling into violence, some smashing windows and breaking into stores. So many people taking off with what they could grab inside. That tension in clear view tonight, this image from St. Louis late today, protestors face-to-face with police in riot gear. ABC Steve osunsami on the 18-year-old who was supposed to begin college today, what he was accused of and the mayor tonight who says if the officer did something wrong, he wants accountability. Reporter: Look closely, this was the peaceful protest another the Ferguson, Missouri police department today. Close to 500 demonstrators nearly spitting in the eyes of police dressed in riot gear, demanding authorities charge one of their own with the murder of 18-year-old Michael brown. They're killing our young people. It's got to stop. Reporter: And this was the chaos that put the city on the map Sunday night. Teams of thieves using the protest as an excuse to steal jeans, shoes, and expensive tire rims. We could no longer stand and watch the looting and destruction of property that was happening. Reporter: Details in great debate and the FBI running its own interview. Neighbors believe the 18-year-old was stealing Saturday afternoon and police were called. We're told that's why they burned the store to the ground. Around the block he was walking with friend to his grandparent's house when police Roland up. He said get the F on the sidewalk. Another witness recorded what she could on the cell phone and turned it over to police. He turned around with his arms in the air and they shot him and he went down. Reporter: Police say at least one of the men physically assaulted the officer, pushing him into his car and going for his gun. It was a physical altercation within the police car between the subject and the police officer at the present time that extended eventually out into the street. This is one of our officers. If he did something wrong, obviously I want accountability. Reporter: Brown's mother beyond devastated but hoping for peace in the city this evening sfl I just wish I could have been there 0 to help him. Reporter: The owner of this beauty shop and the wireless store next door say they understand, a young man was killed, but it led to all of this and they worry this could

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